Recently there has been perfected an implantable prosthetic device in the nature of an infusate pump or so-called artificial gland for dispensing infusates such as durgs and hormones at a very low flow rate to a selected site in the human body over the long term. Eventually the fluid reservoir in such a pump empties so that, if the pump is to continue performing its function, its reservoir must be refilled with a fresh supply of infusate. To avoid having to operate on a patient to remove the pump in order to refill it periodically, the pump is designed with a penetrable self-sealing septum in a wall of the pump which normally seals a passage leading to the pump reservoir.
With the pump implanted in the patient's body so that the septum underlies the skin, the pump can be refilled, as needed, simply by injecting a fresh supply of infusate by means of a hypodermic needle through the patient's skin, through the pump septum and into the infusate chamber inside the device. In some cases, the act of refilling the pump also recharges its power supply so that the pump can operate uninterruptedly for a prolonged period. Implantable pumps such as this are disclosed, for example, in U.S. Pat. Nos. 3,731,681 and 3,851,147.
It is apparent from the foregoing that if the pump is to have a long service life after it is implanted in the body, the penetrable septum must be capable of retaining its sealing properties even after a large number of injections. In other words, the hypodermic needle used to inject the infusate into the pump must not "core" the septum so as to create possible avenues of leakage therethrough.
Also, it is essential that the needle end of the infusate injection apparatus be seated at the proper charging location in the pump before infusate flow is commenced. By the same token, the flowing needle must not be pulled out of the septum as the refilling operation proceeds. Otherwise, the infusate being injected may not flow into the pump reservoir as it is supposed to. Rather, it may be deposited locally in the patient's body. Accordingly, unbeknownst to the patient and the physician, the pump may not be refilled completely and may therefore run out of infusate prematurely with possible adverse consequence to the patient. Additionally, the deposition of a relatively large quantity of infusate locally into the patient might also prove detrimental to the patient.
Bearing in mind that such implantable devices actually move to some extent in the patient's body and that the pump may be situated at different depths below the skin depending upon the weight of the patient, properly seating and maintaining the needle end of the injection apparatus in the pump's recharging station is not a simple matter using a standard hypodermic syringe.